function sys=obv(t,x,zt,ut)
sys=zeros(4,1);

mH=0.285;mL=0.065;l=1.12;g=9.8;

m = mH + mL;
mc14 = mL*l*cos(fi)*cos(fi); mc41 = mL*l*cos(fi)*cos(fi);
mc15 =-mL*l*sin(fi)*sin(th); mc51 =-mL*l*sin(fi)*sin(th);
mc25 = mL*l*cos(th); mc52 = mL*l*cos(th);
mc34 = mL*l*sin(fi)*cos(th); mc43 = mL*l*sin(fi)*cos(th);
mc55 = mL*l^2; mc44 = mL*l^2*cos(th)^2;
mc35 = mL*l*cos(fi)*sin(th); mc53 = mL*l*cos(fi)*sin(th);
Vc14 =-mL*l*(sin(fi)*cos(th)*dfi + cos(fi)*sin(th)*dth);
Vc15 =-mL*l*(sin(fi)*cos(th)*dth + cos(fi)*sin(th)*dfi);
Vc34 = mL*l*(cos(fi)*cos(th)*dfi + sin(fi)*sin(th)*dth);
Vc35 = mL*l*(cos(fi)*cos(th)*dth + sin(fi)*sin(th)*dfi);
Vc25 =-mL*l*sin(th)*dth;
Vc44 =-mL*l^2*sin(th)*cos(th)*dth;
Vc45 =-mL*l^2*sin(th)*cos(th)*dfi;
Vc54 = mL*l^2*sin(th)*cos(th)*dfi;
Gc13 = (mH + mL)*g;
Gc14 = mL*l*g*sin(fi)*cos(th);
Gc15 = mL*l*g*cos(fi)*sin(th);

M = [m 0 0 mc14 mc15 ;0 m 0 0 mc25 ;0 0 m mc34 mc35;mc41 0 mc43 mc44 0;mc51 mc52 mc53 0 mc55];
V = [0 0 0 Vc14 Vc15;0 0 0 0 Vc25;0 0 0 Vc34 Vc35;0 0 0 Vc44 Vc45;0 0 0 Vc54 0];
G = [0;0;Gc13;Gc14;Gc15];
F = [fx;fy;fz;0]; 

k1 = lamb2*(V*dq + G - dM*dq - F - D1 ) + alpha2*lamb1^(2*m2-1) + lamb3*sign(lamb1); 
D1 = k1 + lamb2*M*dq;
